A wide variety of isolation systems have been developed for providing isolation between a test probe and other test equipment to eliminate electrical disturbances that may tend to compromise the accuracy of the test measurement. Some of these known isolation systems optically isolate the sensing probe from the measurement instrumentation by transmitting the input signal to a receiver over a fiber optic medium. It is of course the object of these devices to prevent the passage of any electrical signals from the transmitter unit to the receiver unit unless they are part of the input signal from the device under test sensed by the test probe.
One such example is the "Fiber Optic Isolation System" manufactured by Tektronix, Inc. under the part number A6905S. This device, claimed to be the highest performance isolation system available, has a frequency bandwidth which is limited to 100 megahertz and a maximum working voltage of 850 volts. Consequently, the use of this device for making satisfactory electrical measurements while the device is being subjected to high power electrical disturbances such as high voltage surges or transients, electromagnetic interference, and/or electrostatic discharge, is ineffective.
Although the above device provides an independent battery source for powering the transmitter to avoid a galvanic connection to earth, the separation between the sensing probe and the transmitter unit, as well as the relatively large surface area of the transmitter unit case re-establishes undesired common mode ground loops, increases capacitive loading on the device under test, and increases electromagnetic radiation sensitivity of the measuring equipment, resulting in inaccurate and often unreliable measurements. These undesirable effects, coupled with the lack of necessary shielding makes its use in high power compliance testing prohibitive.
Another device, U.S. Pat. No. 5,181,026 issued to Granville, discloses a measurement system for monitoring various parameters of a high voltage transmission line. The sensed data is converted into modulated light using light emitting diodes, and transmitted to a ground-based receiver over a fiber optic cable. However, the Granville device is intended to be fixedly connected in series with a high voltage power-line, and therefore lacks portability or applicability in benchtop product compliance testing where multiple measurements are taken. Further, although a high voltage measurement is anticipated, the frequency response is fixed at 60 hertz alternating current.
There are prior art devices which utilize the concepts described above but which fall short of making satisfactory electrical measurements while the device is being subjected to high power electrical disturbances. Current methods implement the "trial and error" approach by creating the disturbance and hypothesizing about the resulting effect without any direct observation.
None of the prior art devices teach an isolation system which has a frequency response from DC to 1 gigahertz and which allows observation of signal parameters such as current and voltage in either an analog or digital waveform while the circuit is undergoing high power compliance testing. There are no known devices which have electromagnetic interference immunity to be able to monitor signals with usable accuracy and reliability.